%DEMOENVELOPE shows how to use function envelope to obtain the  
%   upper/down envelope of a given data and plot the envelope. 
% 
%   See also EVELOPE 
 
%   Designed by: Lei Wang, <WangLeiBox@hotmail.com>, 11-Mar-2003. 
%   Last Revision: 21-Mar-2003. 
%   Dept. Mechanical & Aerospace Engineering, NC State University. 
% $Revision: 1.1 $  $Date: 3/21/2003 10:38 AM $ 
 
clc; 

% Load a signal waveform 
%-------------------------------------------- 
% load data.txt data; 
% t = data(:,1); % time series 
% y = data(:,2); % signal data 
% load data.txt data; 
t = fd; % time series 
y = dct_abs; % signal data 
Hd = lowpassfilter2;
y = filter(Hd,y);
figure(1); 
plot(t,y,'b-');  
title('The original signal waveform','FontSize',18); 

% Call function envelope to  
% obtain the envelope data 
%-------------------------------------------- 
[up,down] = envelope(t,y,'spline'); 

% Show the envelope alone 
%-------------------------------------------- 
figure
plot(t,up); hold on; 
plot(t,down); 
title('The envelope of the given signal data','FontSize',18); 
hold off; 

% Show the original signal and its envelope 
%-------------------------------------------- 
figure
plot(t,y,'b'); hold on; 
plot(t,up,'r-.'); 
plot(t,down,'r-.'); 
title('The envelope vs the given signal data','FontSize',18); 
hold off; 